1. Field of the Invention
The present invention relates to a device to control a gas-fired appliance, in particular a gas engine, as a function of the composition of a gaseous fuel.
2. Prior Art
Gas engines are used to an increasing extent in packaged cogeneration systems for local power and heat energy supplies. In this connection, questions of engine operation in existing plants and the selection and/or design of future engine units are also dependent upon the properties of the gaseous fuel supplied. For internal combustion gaseous fuels must meet certain requirements, such as sufficient energy content and high knock resistance. A fuel too low in knock resistance leads to knocking combustion, possibly causing serious damage to the engine and increased pollutant emissions. The decisive criterion for rating the knock resistance of gaseous fueles is the methane numbered (MN). The gaseous fuel supplied to the gas engine has an available methane number (MNA) dependent upon its composition. In public gas supplies today almost exclusively natural gas is used, albeit with varying properties. For peak shaving, local gas utilities blend natural gas with liquid petroleum gas and/or petroleum gas/air mixtures. This measure naturally influences the gas properties, in particular the MNA of the gaseous fuel. To ensure safe engine operation the MNA must always be at least equal to the methane number requirement (MNR) of the gas engine. The methane number required by the engine is affected by design and operating parameters, with the adjustment of the MNR being achieved by changing engine operation. Changes in ignition timing, air/fuel ratio and output are effective measures to reduce the MNR at a decreasing MNA of the gaseous fuel.
The dependence of safe operation upon the properties of the gaseous fuel is also of major importance for other gas-fired appliances, such as burner arrangements.